This invention relates to fluid operating apparatus for positioning of load devices and in particular to a pneumatic operating apparatus having speed change control for moving relatively heavy loads, such as heavy duty industrial, commercial, and refrigerator doors and other closure members.
Fluid driven positioning apparatus is widely employed in industry for rapidly and reliably positioning of various types of loads, including valves, dampers, machine operating elements as well as various closure members. In the institutional and commercial field, automatic door closures may employ fluid driven operators for automatic closing and opening of the doors in response to an appropriate input signal. The operators may be either hydraulic or pneumatic operated. Pneumatic driven door operators may employ air supplies which are generally available in other parts of the institution or which can be readily supplied. Pneumatic systems also are highly desirable in connection with the convenient method of exhausting of the system to the atmosphere.
In such operators, and particularly in connection with door operators, the controlled movement of the door is extremely important to permit safe movement of personnel and associated equipment. Thus, the operator desirably provides relative rapid movement of the door without, however, creating dangerous conditions. This, of course, is particularly significant in heavy door installation such as encountered in industrial and commercial application. Thus, if an operator should be opening or closing a door and during the movement, a vehicle such as a forklift unit attempts to move through the opening without allowing adequate clearance, interengagement could cause severe damage to the door structure and/or the vehicle structure. The large mass of industrial and/or commercial door structure also requires that the velocity and deceleration of the door be controlled both during opening and closing to prevent possible damaging of the door mechanism.
Conventionally, pneumatic or fluid operators include controlled damping means built into the operator. For example, the conventional pneumatic cylinder will normally have the terminal portion of the piston stroke cushioned by a fluid volume of air within the terminal portion of the chamber and may be provided with a special damping chamber mechanism to permit control of the damping characteristic. Such conventional methods although operable do require relatively rugged special construction in order to compensate for the significant stresses and mechanical loads which may be encountered particularly when the piston rod directly interacts with the damping mechanism. Further, most operators are especially designed for particular applications and require relatively expensive custom installation. Although other forms of controls including metering means have been suggested, they have, for one reason or another, not found significant application and there is a great need for a rugged, reliable controlled door operator for providing controlled acceleration and deceleration of the door.